The act is rarely enforced, but Spitzer was known to use obscure laws to go after his enemies, so who knows?
I found this interesting:
The first person prosecuted under the act was heavyweight boxing champion Jack Johnson, who had an affair with a prostitute named Lucille Cameron. Johnson married Cameron so that she couldn't be made to testify against him. Belle Schreiber, a prostitute that had at some point left a brothel and traveled with him to another state, was the next in line to testify against Johnson. He was eventually prosecuted and sentenced to the maximum penalty of a year and a day in prison.